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Implementing 2Descent for Jacobians of Hyperelliptic Curves
 Acta Arith
, 1999
"... . This paper gives a fairly detailed description of an algorithm that computes (the size of) the 2Selmer group of the Jacobian of a hyperellitptic curve over Q. The curve is assumed to have even genus or to possess a Qrational Weierstra point. 1. Introduction Given some curve C over Q , one w ..."
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Cited by 49 (16 self)
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. This paper gives a fairly detailed description of an algorithm that computes (the size of) the 2Selmer group of the Jacobian of a hyperellitptic curve over Q. The curve is assumed to have even genus or to possess a Qrational Weierstra point. 1. Introduction Given some curve C over Q , one would like to determine as much as possible of its arithmetical properties. One of the more important invariants is the MordellWeil rank of its Jacobian J , i.e., the free abelian rank of J(Q ) (finite by the MordellWeil Theorem). There is no algorithm so far that provably determines this rank, but it is possible (at least in theory) to bound it from above by computing the size of a suitable Selmer group. It is also fairly easy to find lower bounds by looking for independent rational points on the Jacobian. (It can be difficult, however, to find the right number of independent points, when some of the generators are large.) With some luck, both bounds coincide, and the rank is determined. In...
Cycles of quadratic polynomials and rational points on a genus 2 curve
, 1996
"... Abstract. It has been conjectured that for N sufficiently large, there are no quadratic polynomials in Q[z] with rational periodic points of period N. Morton proved there were none with N = 4, by showing that the genus 2 algebraic curve that classifies periodic points of period 4 is birational to X1 ..."
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Abstract. It has been conjectured that for N sufficiently large, there are no quadratic polynomials in Q[z] with rational periodic points of period N. Morton proved there were none with N = 4, by showing that the genus 2 algebraic curve that classifies periodic points of period 4 is birational to X1(16), whose rational points had been previously computed. We prove there are none with N = 5. Here the relevant curve has genus 14, but it has a genus 2 quotient, whose rational points we compute by performing a 2descent on its Jacobian and applying a refinement of the method of Chabauty and Coleman. We hope that our computation will serve as a model for others who need to compute rational points on hyperelliptic curves. We also describe the three possible Gal(Q/Q)stable 5cycles, and show that there exist Gal(Q/Q)stable Ncycles for infinitely many N. Furthermore, we answer a question of Morton by showing that the genus 14 curve and its quotient are not modular. Finally, we mention some partial results for N = 6. 1.
Large Torsion Subgroups Of Split Jacobians Of Curves Of Genus Two Or Three
 FORUM MATH
, 1998
"... We construct examples of families of curves of genus 2 or 3 over Q whose Jacobians split completely and have various large rational torsion subgroups. For example, the rational points on a certain elliptic surface over P of positive rank parameterize a family of genus2 curves over Q whose Jac ..."
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We construct examples of families of curves of genus 2 or 3 over Q whose Jacobians split completely and have various large rational torsion subgroups. For example, the rational points on a certain elliptic surface over P of positive rank parameterize a family of genus2 curves over Q whose Jacobians each have 128 rational torsion points. Also, we find the genus3 curve ) = 0, whose Jacobian has 864 rational torsion points.
Explicit 4descents on an elliptic curve
 Acta Arith
, 1996
"... Abstract. It is shown that the obvious method of descending from an element of the 2Selmer group of an elliptic curve, E, will indeed give elements of order 1, 2 or 4 in the WeilChatelet group of E. Explicit algorithms for such a method are given. 1. ..."
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Abstract. It is shown that the obvious method of descending from an element of the 2Selmer group of an elliptic curve, E, will indeed give elements of order 1, 2 or 4 in the WeilChatelet group of E. Explicit algorithms for such a method are given. 1.
Computational Aspects of Curves of Genus at Least 2
 Algorithmic number theory. 5th international symposium. ANTSII
, 1996
"... . This survey discusses algorithms and explicit calculations for curves of genus at least 2 and their Jacobians, mainly over number fields and finite fields. Miscellaneous examples and a list of possible future projects are given at the end. 1. Introduction An enormous number of people have per ..."
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Cited by 14 (3 self)
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. This survey discusses algorithms and explicit calculations for curves of genus at least 2 and their Jacobians, mainly over number fields and finite fields. Miscellaneous examples and a list of possible future projects are given at the end. 1. Introduction An enormous number of people have performed an enormous number of computations on elliptic curves, as one can see from even a perfunctory glance at [29]. A few years ago, the same could not be said for curves of higher genus, even though the theory of such curves had been developed in detail. Now, however, polynomialtime algorithms and sometimes actual programs are available for solving a wide variety of problems associated with such curves. The genus 2 case especially is becoming accessible: in light of recent work, it seems reasonable to expect that within a few years, packages will be available for doing genus 2 computations analogous to the elliptic curve computations that are currently possible in PARI, MAGMA, SIMATH, apec...
Descents on Curves of Genus 1
, 1995
"... This thesis is available for Library use on the understanding that it is copyright material and that no quotation from the thesis may be published without proper acknowledgement. I certify that all the material in this thesis which is not my own work has been clearly identified and that no material ..."
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Cited by 8 (4 self)
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This thesis is available for Library use on the understanding that it is copyright material and that no quotation from the thesis may be published without proper acknowledgement. I certify that all the material in this thesis which is not my own work has been clearly identified and that no material is included for which a degree has previously been conferred upon me.
Powerfree values, large deviations, and integer points on irrational curves
 JOURNAL DE THÉORIE DES NOMBRES DE BORDEAUX
, 2006
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Pencils of quadrics and the arithmetic of hyperelliptic curves
"... (with an appendix by Tim and Vladimir Dokchitser) ..."
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EXPLICIT SELMER GROUPS FOR CYCLIC COVERS OF
"... Abstract. For any abelian variety J over a global field k and an isogeny φ: J → J, the Selmer group Sel φ (J, k) is a subgroup of the Galois cohomology group H 1 (Gal(k s /k), J[φ]), defined in terms of local data. When J is the Jacobian of a cyclic cover of P 1 of prime degree p, the Selmer group h ..."
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Abstract. For any abelian variety J over a global field k and an isogeny φ: J → J, the Selmer group Sel φ (J, k) is a subgroup of the Galois cohomology group H 1 (Gal(k s /k), J[φ]), defined in terms of local data. When J is the Jacobian of a cyclic cover of P 1 of prime degree p, the Selmer group has a quotient by a subgroup of order at most p that is isomorphic to the ‘fake Selmer group’, whose definition is more amenable to explicit computations. In this paper we define in the same setting the ‘explicit Selmer group’, which is isomorphic to the Selmer group itself and just as amenable to explicit computations as the fake Selmer group. This is useful for describing the associated covering spaces explicitly and may thus help in developing methods for second descents on the Jacobians considered. 1.
Computing the MordellWeil rank . . .
, 1992
"... We derive the equations necessary to perform a 2descent on the Jacobians of curves of genus two with rational Weierstrass points. We compute the MordellWeil rank of the Jacobian of some genus two curves defined over the rationals, and discuss the practicality of using this method. ..."
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We derive the equations necessary to perform a 2descent on the Jacobians of curves of genus two with rational Weierstrass points. We compute the MordellWeil rank of the Jacobian of some genus two curves defined over the rationals, and discuss the practicality of using this method.